Fluid pressure braking system



INVENTOR. B/Yrfefer C Bon/5N ww 0% i l H Ilww xml Illll'llllllllll miluwnnmn ATTORNEY.

Feb. 24, 1942.

H. c. BQWEN FLUIDA PRESSURE BRAKING SYSTEMv Filed Feb. 7, 1940 y Patented Feb. 24,

UNITED A'srxrlezs PATENT "ori-ICE 2,273,924 v FLUD PRESSURE BRAKING SYSTEM Herbert C. Bowen, Detroit, Mich., assignor to Hydraulic Brake Company, Detroit, Mich.,

poration of California Application February 7, 1940, Serial No. 317,741 A (ol. '6o-54.6)

1 Claim.

This invention relates tofluid pressure braking systems, and more particularly to fluid pres'- sure producing devices for such systems.

Broadly the invention comprehends a uid pressure braking system including a fluid pressure producing device operative to increase pressure on the fluid in the system Without proportionately increasing the applied. actuating force.

In the illustrated embodiment of the invention, the system includes a iluid pressure producing device comprising a low pressure producing means and a high pressure producing means,

ffa'nd means actuated bythe device. During initial actuation of the device a large volume. of fluid is displaced under low pressure to quickly of a large volume of fluid is not materially ef-4 fected until transition from low to high pressure is accomplished, and thereafter, uid is metered from the low pressure producing means proportionately to increase of pressure on the fluid in the low pressure producing means so as to render it ineffective for producing pressure.

An object of the invention is to distribute the transition from low to high pressure over a wide range so as to smooth out the operation of the system.

Another object is to provide a fluid pressure system including means controlled by pressure in the system for effecting gradual transition from low to high pressure.

A further object of the invention is to providey a lluid pressure system including means cona col- Other objects and ,advantages of the invention will appear from the following description taken in connection with the accompanying drawing forming a part of this specification, and in Whichy l l Fig. -1 is a schematic view of a fluid pressure braking system embodying the invention; and

Fig. 2 is a vertical sectional view of the uid pressure producing device. 1 y

Referring to the 'drawing Vfor more specific details of the invention, I0. represents a uid pressure producing device including a reservoir I2 having a filling opening i4,.n orma1ly closed as by a plug I6 provided with openings I8 for venting the reservoir to the atmosphere. The plug I6 has therein a perforated diaphragmvZB, and a baille plate 22 depended from -the diaphragm servestoinhibit lluid from splashing through the openingsv I8;-

Formed at the base vof the .reservoir is a cylinl a large chamber 32 and a relatively small cham-v ber 34. The sleeve 30 has a circumferential portion of reduced diameter providing in conjunction with the wall of the cylinder an annular trolled by pressure in the system for, disassociating the low pressure producing means from the high pressure producing means.

A feature of the invention is a pressure producing device including a cylinder having a large chamberand a relatively small chamber, a piston movable in each of the chambers for creating pressures, and a restricted passage through the piston in the largel chamber for continuously mechamber or passage' 36 communicating with the large chamber 32, and a port 38 in the reduced portion of the sleeve provides a communication between the annular chamber 36 and the small,

chamber 34. The outer end of the sleeve 30 i's closed by a head 48 provided with a discharge port 42 controlled as by a two-way valve 44.

A iluid pressure delivery pipe or conduit 46 suitably connected to the discharge port 42 has branches connected respectively to fluid pressure actuated motors 48, preferably arranged in pairs, one pair for actuating brakes associated with the vfront wheels of a motor vehicle, and another' for actuating brakes associated with Vthel rear .wheels of the vehicle..

The brakes may be of a conventional type, such as shown in the patent to L. S. Watres, No. 853,848, May 14,1907. Brake structures of this type and many other types, includingv a rotatable dnlm and afriction element for cooperation therewith. inherently have, when the brake is at rest or im retracted position, a rather large clearance between the friction element and the drum, requiring substantial initial movement of the friction element before effective engagement of the element with the drum. It is highly desirable that the initial movement of the friction element necessary to take up this clearance between the drum and the friction element be effected quickly, and to accomplish this it becomes desirable to displace av large volume of fluid under low pressure for activating the friction elements into drum engagement, and thereafter to displace a relatively small volume of fluid under high pressure.

In the illustrated embodiment, each of the brakes includes a fixed support or backing plate 50, a rotatable drum 52 associated with the backing plate, a pair of corresponding friction elements or shoes 54 pivotally mounted on the backing plate for cooperation with the drum, a retractile spring 56 connecting the shoes, and a fluid pressure actuated motor corresponding to the motors 48 for actuating the shoes into engagement with the drum against the resistance of the retractile spring.

A piston 58 reciprocable in the cylinder 24 is held against displacement by a washer 60 seated on an annular shoulder 62 in the open end of the cylinder and heldin place by a retaining ring 64 fitted in a groove in the wall of the cylinder. The Piston 58 has a head 66, a reduced body portion 68 providing in conjunction with the walls of the cylinder an annular chamber 'I0 communicating with theoeservoir by way of the cylinder past the piston. The head 66 of thepiston has a plurality of spaced passages 16 therethrough providing communications between the vannular chamber 10 and that portion of the cylinder forward of the piston, and a sealing cup 18 seated on the head controls the passages.

An extension 80 arranged 'concentrically on the piston 58 has thereon a piston 82 reciprocable in the chamber 34. The extension and pistons are bored to provide a passage 86 communicating with the annular chamber 10, also with the chamber 32 by way of a restricted port 88. As shown, the port 88 is restricted as by a calibrated wire 90 inserted therein, bent over, and spotwelded or otherwiseiastened to the extension so as to secure the wire against displacement. A l

plug 82 is pressed in that end of the passage 86 opening through the piston 82 so as to present a-smooth unbroken face on the piston,.and a plurality of spaced passages 94 through the piston 82 provide communications between the chambers 32 and 34. A sealing cup 86 seated on the head of the small piston 82 controls the passages 94 through the piston, and la spring 88 interposed between the cup 96 and the two-Way valve 44 `serves to retain the cup and valve against displacement and also to return the pisfoot pedal lever llt, force ls transmitted therefrom through the rod |08 and thrust pin |82 to the piston 58, resulting in advancing the pistons on the compression stroke. During the initial movement of the pistons on the compression stroke, the cup 18 on the large piston 58 covers the port 28, and the cup 98 on the small piston 82 covers the port 38. Thereafter, as the pistons advance on the compression stroke, the fluid in the chamber 32 is displaced therefrom through l the passages 84 1n the small piston 82, past the cup 96 in the small chamber 34, thence past the two-way valve 44, through the discharge port Q2 and fluid pressure delivery pipe or conduit 46 into the fluid pressure actuated motors 48, causing,energization of the motors and resulting in rapid movement of the friction elements or shoes 54 into engagement with the drums 52 against the resistance of the retractile springs 56.

During this operation, uid in the chamber 32 is also being displaced therefrom through the restricted passage or port 88 into the passage 86, and through the latter passage into the annular chamber l0, thence through the port 26, into the reservoir I2. The fluid displaced through the re- A stricted passage does not perceptibly relieve the pressure on the fluid during the initial movement of the pistons on the compression stroke,

hence a large volume of fluid is displaced, resultlng in rapidly actuating the friction elements or shoes into engagement with the drum,v

and, thereafter, as the pistons advance on the compression stroke, the resistance offered by engagement of theshoes with the drum results in increase of pressure on the uid and consequent increase in the flow of fluid from the large chamber 32 through the restricted passage 88 to such an extent as to gradually transfer the pressure on the fluid in the system from the large piston 58 to the small piston 82. This transfer is effe'cted over a wide range, and consequently is not perceptible to the operator.

Upon completion of a braking operation, the

I foot pedal lever ||0 is released and is returned tons to retracted position against the washer 60 cylinder 24 for the exclusion of dust and other foreign substances. A rod |08 has one of its ends connected to the coupling |04, and its other end pivotally connected to a foot pedal lever EEO rockably mounted as at ||2, and connected by a retractile spring I4 to a xed support H6.

In a normal operation, upon depressing the to its retracted position under the influence of the retractile spring H4. This mo"ement of the foot pedal lever retracts the vrod |88 and thrust pin |82 with the resultant release of the pistons and return thereof to retracted position under the influence of the spring. 98.

As the pistons return to retracted position, a partial vacuum is created in the chamber 32. This results in drawing fluid from the reservoir through the supply port 26, into the annular chamber lll, thence through the passages 'I6 in the head of the large piston 58, past the sealing cup i8, into the large chamber 32, thence through the passages 94 in the head of the small piston 82, past the sealing cup 96, into the small chamber 34, completely filling the chambers 32 and 34.

During this operation, fluid is returning to the chamber 34 from the fluid pressure actuated motors 48 and the fluid pressure delivery pipes connecting the motors to the chamber 34. This may result in the chamber 34 receiving a quantity of fluid in excess of its capacity, and in this event the excessive quantity f iluid received by the chamber is displaced theiqfrom through the port 38 into the large chamber 32, thence thi ough the port 28, into the reservoir.

While this invention hasabeen described in connection with certain specific embodiments, the principle involved is susceptible of numerous other applications thatwill readily occur to persons skilled in -the art. The invention is, therefore, to be limited only as indicated'by th scopeof the appended claim. Having thus described the various features of the invention, what I claim as new and desire to secure by Letters Patent is- -A uid pressure device having a high pressure chamber, and a low pressure chamber discharging` into -the high pressure chamber, a piston movable in each of the chambers for' creating 10 pressure, and means for relieving the pressurein the low pressurev chamber as the pistons advance including an open passage interconnecting the low pressure chamber and the reservoir,

a restricting wire disposed in said passage to reduce the effectivearea thereof to a value such that it will be too small to relieve the pressure 1n the low pressure chamber so long as the piston therein has any substantial movement f HERBERT C. BOWEN. 

